1. Field of the Invention
The present invention relates to an organozirconium compound and an organic solution comprising the compound for the preparation of a zirconium-containing thin film by the Metal Organic Chemical Vapor Deposition method (referred to as MOCVD hereinafter), and also relates to a zirconium containing thin film formed using the organozirconium compound and an organic solution of the compound. More particularly, the present invention relates to an organozirconium compound and an organic solution comprising the compound for preparing a Pb(Zr,Ti)O3 (referred to as PZT hereinafter) thin film by the MOCVD method in the preparation of ferro-electric memories.
2. Description of the Background
An organozirconium compound which is known to be useful in the MOCVD method (referred to as MOCVD-organozirconium compound hereinafter) is zirconium tetra(2,2,6,6-tetramethyl-3,5-heptadionate) (referred to as Zr(thd)4 hereinafter). Another compound known to be useful in the MOCVD method is the organolead compound, lead bis(2,2,6,6-tetramethyl-3,5-heptadionate) (referred to as Pb(thd)2 hereinafter). Still another useful compound in the MOCVD method is diisopropoxy titanium bis(2,2,6,6-tetramethyl-3,5-heptadionate) (referred to as Ti(iPro)2(thd)2 hereinafter).
However, it is reported that Zr(thd)4, as an MOCVD-organozirconium compound, exhibits the problem that the film deposition temperature of Zr(thd)4 deviates from the temperatures of the other two compounds when forming a PZT thin film, since Zr(thd)4 has a higher decomposition temperature in comparison to that of Pb(thd)2, which is an MOCVD-organolead compound and that of Ti(iPro)2(thd)2, which is an MOCVD-organotitanium compound (Anthony C. Jones et al., Journal of the European Ceramic Society, 19 (1999) 1431-1434). To solve this problem, it has been proposed to use tetratertiarybutoxy zirconium (referred to as Zr(tBuO)4 hereinafter) in this role, since it has a low decomposition temperature. However, this compound is extremely reactive with the air, and therefore, has the different problem of being extremely difficult to handle.
Compared to this, published PCT application WO98/51837 (PCT application number: PCT/GB98/01365), describes new organozirconium compounds which are useful in the MOCVD method, which are diisopropoxy zirconium bis(2,2,6,6-tetramethyl-3,5-heptadionate) (referred to as Zr(iPrO)2(thd)2 hereinafter), ditertiarybutoxy zirconium bis(2,2,6,6-tetramethyl-3,5-heptadionate) (referred to as Zr(tBuO)2(thd)2 hereinafter), Zr2(iPrO)6(thd)2, and the like. These compounds are superior to the above-described conventional compounds in that they can be used for film deposition over a wide temperature range.
In the meantime, Okuhara et al., have proposed a new organozirconium compound for the MOCVD method which is isopropoxy zirconium tris(2,2,6,6-tetramethyl-3,5-heptadionate) (referred to as Zr(iPrO)1(thd)3 hereinafter). This compound exhibits a high vapor pressure as a monomer and is readily soluble in a solvent (47th Applied Physics-related Joint Lectures, Preliminary Report, (March, 2000), p.540).
However, organozirconium compounds such as Zr(iPrO)2(thd)2, Zr(tBuO)2,(thd)2, and Zr2(iPrO)6(thd)2, which are described in published PCT application WO98/51837, exhibit the problem of tending to react with the above-described Pb(thd)2 and similar compounds, leaving large amounts of unvaporized residues at vaporization, when the compounds are mixed with them in order to form a PZT thin film by the MOCVD method.
Regarding the organozirconium compounds represented by Zr(iPrO)1(thd)3 described by Okuhara et al. above, they leave large amounts of residue upon vaporization. Moreover, if the compounds are mixed with other compounds such as Pb(thd)2, they also tend to react with each other, further increasing residues upon vaporization. This poses another problem.
Accordingly, one object of the present invention is to provide an organozirconium compound having a decomposition temperature which is lower in comparison to those of the above-described conventional MOCVD organozirconium compounds and which is near to the decomposition temperatures of MOCVD organolead compounds and organotitanium compounds.
Another object of the present invention is to provide an organozirconium compound which, upon vaporization, only leaves a small amount of residue.
Still another object of the present invention is to provide an organozirconium compound which only reacts with difficulty with either one or both of an MOCVD organolead compound and an MOCVD organotitanium compound and, when mixed with these compounds and upon vaporization of the mixture, leaves only a small amount of residue.
Yet another object of the present invention is to provide an organic solution which enables more accurate control of the composition of a PZT thin film.
Still another object of the present invention is to provide a zirconium-containing thin which is uniform and easily controllable.
Briefly, these objects and other objects of the present invention as hereinafter will become more readily apparent can be attained by an organozirconium compound which comprises zirconium combined with xcex2-diketone compounds and an alkoxy group having a branched alkyl group, and which is represented by formula (1): 
wherein R is a branched alkyl group having 4 or 5 carbons; and L1, L2, and L3, are the same or different from each other, and each are a xcex2-diketone compound.
Since the central metal in the organozirconium compound of the first aspect of the present invention has an alkoxy group having a bulky branched alkyl group and xcex2-diketone compound ligands coordinated to the zirconium atom at a metal to ligand ratio of 1:3, the compound itself leaves only small amounts of residues upon vaporization of the complex. For the same reason, the complex has a decomposition temperature near those of organolead compounds and organotitanium compounds, and when mixed with them, it is hard to react the zirconium complex with the organolead compounds and organotitanium compounds, leaving only small amounts of residues upon vaporization.
The second aspect of the present invention is an organic solution comprising the organozirconium compound of the first aspect of the present invention dissolved in an organic solvent together with either one or both of Pb(thd)2 and Ti(ORxe2x80x2)2(thd)2. The second aspect of the present invention also encompasses an organic solution comprising an organozirconium compound of the first aspect of the present invention dissolved in an organic solvent together with either one or both of Pb(tod)2 and Ti(ORxe2x80x2)2(tod)2. Here, thd is a 2,2,6,6-tetramethyl-3,5-heptadionate group, tod is a 2,2,6,6-tetramethyl-3,5-octadionate group, and Rxe2x80x2 is a straight-chain or branched alkyl group having 3 to 5 carbons.
During film deposition, the organic solution comprising an organozirconium compound of the first aspect of the present invention, which is mixed and dissolved in an organic solvent together with Pb(thd)2, Ti(ORxe2x80x2)2(thd)2, Pb(tod)2, or Ti(ORxe2x80x2)2(tod)2, does not cause an increase of residues upon vaporization as a result of mixing and, therefore, can be stably supplied to an MOCVD apparatus. Furthermore, since vaporization temperatures and decomposition temperatures of the organozirconium compound, organolead compound, and organotitanium compound are near each other, it is possible to improve control of the composition of a PZT thin film.
The second aspect of the present invention is a raw material solution, wherein Rxe2x80x2 is the same as the branched alkyl group (R) represented in formula (1) shown in the first aspect of the present invention.
By selecting the same group for R and Rxe2x80x2, the problem of exchange of alkoxy groups is solved, and changes in characteristics of the compounds are limited.